Methods and Materials for Improving Cosmetic Finishes Speakers from Polynt Composites Andrea Rebecchi, Technical Service UPR & GC Marco Dainelli, Technical Service UPR & GC

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Methods and Materials for Improving Cosmetic Finishes

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Shrinkage of FRP Resins Mechanisms for shrinkage Stress-free temperature Effect of shrinkage on cosmetics Methods to isolate shrinkage

Methods and Materials for Improving Cosmetics Vinyl ester barrier coats Other methods

Cosmetic Quality of FRP

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The Consumer’s Expectations Automotive/Marine Type Finishes Have Become the Goal

in FRP Manufacturing

The Cost of Print and Distortion

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Rework, air-filing, block sanding, fairing, post-finishing, repairs, QC work, rejects, buffing, patching, re-sprays, P.I.

Cosmetic Standards Are Largely Subjective

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Beauty is in the eye of the beholder Variance in customer expectations

Defining Cosmetic Quality

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Cosmetic surface flaws go by many different names: Print-though, distortion, heat lines, orange peel, dimples, waviness, glass print, wrinkles, pock marks, puckered, poor profile, glass pattern, balsa print, woven roving checks, rough surface, heat distortion All of these terms describe a visible flaw in the smoothness of the surface of a finished fiberglass part. These flaws are usually only cosmetic in nature and rarely disrupt the underlying structure integrity.

Defining Cosmetic Quality

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There are various types of surface distortions that are caused by differentmechanisms. While not all types can be neatly classified, all print and distortion can be group grossly into two sets:

Small-term distortion ( < 0.5 mm ) Long-term distortion ( > 0.5 mm )

Defining Cosmetic Quality

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Small-term distortions are on the size order with flaws (orange peel, fish eyes,etc.) in the coating film thickness ( paint or gel coat )

Small-term distortions show the individual fibers of the layer of reinforcement directly behind the film.

Types of Cosmetic Flaws

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Examples of Small-Term Distortion

Defining Cosmetic Quality

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Long-term distortions are flaws that are larger in size and may even disrupt thesurface enough to be felt. Larger flaws in application of the coating film, such as sag lines or curtaining are long-term distortions. Other common examples are the transfer of patterns of the reinforcing fabrics and cores to the surface.

Measuring Surface Profile

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•Cosmetic surface quantified using Byk Gardner Wavescan Plus

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Sources of Cosmetic Flaws

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Primary source for print is the tooling. Every flawed copy costs more than the tooling to fix.

Methods and Materials for Improving Cosmetic Finishes

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Shrinkage of FRP Resins Mechanisms for shrinkage Stress-free temperature Effect of shrinkage on cosmetics Methods to isolate shrinkage

Methods and Materials for Improving Cosmetics Vinyl ester barrier coats Other methods

Shrinkage

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Unsaturated polyester resin shrinks when it cures A part is slightly smaller than a mold due to: Cure shrinkage – in the mold o Amount depends on the resin, affects dimensions. o Some shrinkage is necessary for demolding. Cooling shrinkage – after exotherm o Amount depends on the stress-free temperature. Post-cure shrinkage – after de-mold o Amount depends on the unfinished cure. o Usually affects cosmetics, not dimensions. Glass and filler content effect the shrinkage

Stress-Free Temperature

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All items expand and contract withchanges in temperature. Temperature changes cause stresses. The temperature at which the resin solidifies has no thermal stress, or the stress-free temperature.

Laminate Thermal Stresses

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High exotherm causes high stress-freetemperatures. High stress-free temperatures cause high thermal stresses when it cools to ambient temperature. Worst thermal case is outdoor winter storage. Low exotherm minimizes thermal stress.

Shrinkage

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All typical thermoset polymers shrink: Gel coat always shrinks Barrier coat always shrinks Skin laminate always shrinks Bulk laminate always shrinks

Reinforced layers shrink less than un-reinforced layers. Differential shrinkage rates can result in warpage.

Conventional UPR

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Linear Shrinkage

Linear Shrink Mold Linear Shrink Mold with Uncured Conventional UPR

Linear Shrink Mold with Cured Conventional UPR

Conventional UPR has

significant linear

shrinkage.

Idealized Laminate Description

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Gel Layer on a Mold Surface

Laminate

Fibers

Stiff Fibers Resist Being Compressed

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Laminate Shrinkage Begins

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If the Gel Coat Stays in Contact with the Mold…

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The shrinkage is driven to the back side.

If Post Cure Shrinkage Occurs… Or if the Gel Coat Softens…..

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The shrinkage occurs on the front side, too

Thick Gel Coat or Barrier Coat Helps Smooth out the Surface…..

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Barrier coats isolate the shrinkage from the surface

The Degree of Shrinkage Affects the Type Distortion

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Small amounts of shrinkage can give “distortion”. More shrinkage gives an apple sauce/orange peel texture. Even more and fiber bundles become visible. Up to and including the “look” of the weave.

Shrinkage Occurs:

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Because of Cure In the mold

Because of Post-cure after De-molding When it wasn’t finished curing

Not enough heat Not enough catalyst and/or promoter Not enough time

Because of Cooling from the Stress-Free Temperature High exotherm is bad

Because of Cure-Shrinkage Stress Relaxation When you get close to the glass transition temperature Happens even when fully cured

Minimizing Shrinkage

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Conventional UPR resin requires a long,slow cure. Complete cure to avoid post-cure. Low exotherm to minimize thermal

stresses. Thinner is better.

Isolate Gel Coat from Resin Shrinkage

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Barrier Coat - Applied like Gel CoatImproves surface profile. Decreases cycle time. Adds material cost & HAP emissions. Proper selection and application improves blister resistance. Allows less expensive bulk resins to be used behind.

Isolate Gel Coat from Resin Shrinkage

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Skin Coat - Applied via spray-up or hand-lay up Improves surface profile. Resin determines blister resistance. Proper selection and application improves

blister resistance and structural integrity. Allows less expensive bulk resins to be

used behind.

Isolate Gel Coat from Resin Shrinkage

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CoreMat, Trivera, Veils Improves surface profile. Extra labor. Not easily conformable.

Methods and Materials for Improving Cosmetic Finishes

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Shrinkage of FRP Resins Mechanisms for shrinkage Stress-free temperature Effect of shrinkage on cosmetics Methods to isolate shrinkage

Methods and Materials for Improving Cosmetics Vinyl ester barrier coats Other methods

Isolate Gel Coat from Resin Shrinkage

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For Long-Term Distortion: •Skin coats resins - Applied via spray-up or hand-lay up

•Sheet goods - Veils, CoreMat, Trivera, etc.

For Short-Term Distortion: •VE barrier coats

Reasons to Use Vinyl Ester Barrier Gel Coats

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Eliminates fiber print-through anddistortion for smooth parts. Reduces osmotic blistering. Increased production rates…More parts per day.

How Barriers Improve Cosmetics

Barrier Coat

Gelcoat

Laminate

Surface Profile of Composite With and Without VE Barrier Coat

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Composite No Barrier

Composite with Barrier

Surface rating before post-cure 8.8 9.2

Surface rating after post-cure 3.8 6.0

Panel was post-cured at 65°C for 72 hours. The laminate is 32mm in thickness and 30% in glass

content of 2,54 cm chopped glass. The surface rating has the scale of 0 to 10.5. The higher

the rating, the better the surface profile.Surface rating is based on the BYK-Gardner Wave-Scan ACTTM orange peel standards.

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Used Below the Waterline ….

• 100 hours exposure to boiling water-superior performance

• 3 years at ambient-zero blisters GEL

COAT

BULK Laminate

H2O H2O

Voids

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THIC

K S

EC

TIO

NTH

IN S

EC

TIO

N

46 52 92

0.5 0.5 0.1

2.0 1.2 0.0

Hours @ 100 C

Blister Rating(Thick)

Blister Rating(Thin)

92

0.2

0.0

STANDARD GEL COAT

NO BARRIER VE BARRIERVE SKIN with FIBER BARRIER + SKIN

VE Barrier Coats Add Toughness

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VE resins have a higher toughness than most gel coats (no pigments and fillers).

Laminates using VE barrier coats crack less than double thickness gel coat.

Improve FRP Cosmetics

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Isolate the gel coat from: Heat Shrinkage

Use VE Barrier Coats: To block short-term distortion Protect from blister formation/print from

laminate voids Use Sprayable Syntactic Foams: To block long-term distortion Hide print from woven roving, core, or putty

lines

SELECTED PRODUCTS

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GEL-COAT POLYCOR HWR SERIES : Advanced technology polyester developed for superior weathering

resistance to surface yellowing and chalking. POLYCOR HWR SERIES offer excellent gloss retention, reduced yellowing, high colour stability, reduced chalking, reduced stress cracking, more resilient surface, low water absorption and high blister resistance.

ARMOFLEX 99 F : Advanced technology polyesters that have been formulated for polyester industry. ARMOFLEX 99 F gel coats have lower volatile organic compounds (VOC’s) than standard gel coats. ARMOFLEX 99F offers good UV resistance for reduced chalking and yellowing in outdoor application, good resistance to water and osmotic blistering, greater transfer efficiency, less overspray and enhanced crack resistance.

BARRIER-COAT EPOVIA OPTIMUM BC 4200 PA : Based on selected vinyl ester resins, BC 4200 PA offers an

improving gel coat cosmetics (reduction of fiber pattern and low shrinkage), good mechanical properties, high distortion temperature, improving hydrolytic performance over the gel-coat products alone.

SELECTED PRODUCTS: Resins

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LAMINATING RESINS DISTITRON® VE 100ST (series available in different viscosity and reactivity) is a thixotropic pre-

accelerated vinylester - resins with excellent mechanical and thermal characteristics providing both low both excellent chemical resistance to prevent blistering formation and low shrinkage to guarantee excellent final cosmetics. In order to comply with ever stricter environmental legislation for VOC emissions a low styrene content version is also available

DISTITRON® VEef220 STZ: the resin contains less than 35% of styrene without including any other monomer in its formulation.

EPOVIA Optimum KRF 4031TA: modified vinylester resin, thixo preaccelerated,, fast curing time, high hardness, low shrinkage to improve aesthetic surface.

INFUSION RESINS DISTITRON® VE 100 SC is a vinylester resin with high thermic-mechanical characteristics, excellent

chemical and hydrolysis resistance, excellent fibreglass wettability and flowing. Due to its special polymer designed for infusion

DISTITRON® VE 370 SC combines low viscosity with lower styrene content without sacrificing mechanical and thermal properties. Both are non-preaccelerated giving maximum flexibility of pot life needed for the infusion depending on amount of Cobalt salts added.

EPOVIA Optimum KRF 4436 AL infusion vinylester resin, preaccelerated, low viscosity, reduced print through

ISO-NPG series were also developed as they can garanteee high mechanical characteristics and very good hydrolysis resistance in application where VE resins can not be used.

Several versions of DISTITRON® 152 are available with different reactivity depending on season and infusion time needed.

The portfolio includes also Orto-DCPD resin like DISTITRON® I100 SV1,5 that can guarantee fast flowing and excellent impregnation of the dry materials.

Cosmetic Quality of FRP

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Using the right methods and materials, FRP can meet the consumers expectations at a lower overall cost!